Advantageously, thermoelectric converters operate reliably for long periods of time at high hot junction temperatures for producing high electrical power outputs, and to this end various systems employing radioisotope heat sources for Si-Ge thermocouples have become useful. In this regard, a heat transfer means, such as a fluid heated by the source, supplies heat to the hot junction of the thermocouple and another heat transfer means, such as a cooled fluid and/or radiator, cools the cold junction of the thermocouple to provide a high temperature differential across the thermocouple, whereby the electrical output of the converter corresponds to the temperature differential across the converter, while the high performance of the thermocouple and a high hot junction temperature has depended on a stable mechanical, chemical and metallurgical configuration.
Report NYO 3582-12, illustrates one example of such a thermoelectric device. As shown, for example in FIG. 3.5-1 of this report, the device comprises both "N" and "P" elements having end pieces, comprising shoes, straps, insulators, contacts, flexible connectors, and hot and cold plates that contain heat transfer fluids that circulate through respective hot and cold plates by means of suitable pumps, heat pipes or the like. The elements (N and P) have the same or different lengths. Similarly, the "N" and "P" elements (legs) of the device and their end pieces have various thicknesses, cross-sections, and cross-sectional areas, e.g. the same or different rectangular cross-sectional areas.